What types of data implement the Copy-on-write mechanism?

The Copy-on-write (COW) mechanism is implemented in some data types to optimize memory and performance. In iOS, this is implemented in:

• NSString and NSMutableString — when a string is copied, a reference to the same object is created, and the actual copying occurs only when an attempt is made to modify the string.
• NSArray and NSMutableArray — similarly, copying an array is lazy, and a separate copy is created when modifications are made.

This allows efficient handling of large data volumes, avoiding unnecessary copying until the data is actually changed.